GPT-6 Astra returns invalid_prompt for harmless prompts across multiple PCs on the same account

What version of the Codex App are you using (From “About Codex” dialog)?

26.901.6511.0

What subscription do you have?

pro

What platform is your computer?

Microsoft Windows NT 10.0.26200.0 x64

What issue are you seeing?

GPT-6 Astra consistently returns invalid_prompt for harmless prompts.

For example, even this prompt:

Reply only with OK

returns:

ERROR: Invalid prompt: your prompt was flagged as potentially violating our usage policy. Please try again with a different prompt: https://platform.openai.com/docs/guides/reasoning#advice-on-prompting

The same happens with simple prompts such as hello.

This issue appears to be account-specific and GPT-6-Astra-specific:

• It reproduces on multiple different computers when using the same OpenAI account.
• GPT-5.6 Sol works normally on the same computers and with the same account.
• GPT-6 Astra fails with both low and max reasoning effort.
• The issue also reproduces from Codex CLI using an ephemeral session with user configuration ignored.

Codex App version: 26.901.6511.0
Codex CLI/runtime version: 0.153.4

This does not appear to be caused by the prompt content, local project, user configuration, reasoning effort, or a specific computer.

What steps can reproduce the bug?

1. Sign in to Codex using the affected OpenAI account.

2. Select gpt-6-astra.

3. Send a harmless prompt such as:

   Reply only with OK

4. Codex returns:

   ERROR: Invalid prompt: your prompt was flagged as potentially violating our usage policy.

The issue can also be reproduced directly with Codex CLI 0.153.4:

codex exec `
  --ephemeral `
  --ignore-user-config `
  --skip-git-repo-check `
  -m gpt-6-astra `
  -c 'model_reasoning_effort="low"' `
  "Reply only with OK"
Result:

OpenAI Codex v0.153.4
model: gpt-6-astra
provider: openai
reasoning effort: low

user
Reply only with OK

ERROR: Invalid prompt: your prompt was flagged as potentially violating our usage policy.

The same result occurs with maximum reasoning effort:

codex exec `
  --ephemeral `
  --ignore-user-config `
  --skip-git-repo-check `
  -m gpt-6-astra `
  -c 'model_reasoning_effort="max"' `
  "Reply only with OK"

Control test with GPT-5.6 Sol:

codex exec `
  --ephemeral `
  --ignore-user-config `
  --skip-git-repo-check `
  -m gpt-5.6-sol `
  -c 'model_reasoning_effort="low"' `
  "Reply only with OK"

Result:

OK

The GPT-6 Astra failure reproduces on multiple different computers when signed into the same OpenAI account.

### What is the expected behavior?

GPT-6 Astra should accept harmless prompts such as `Reply only with OK` and return a normal response instead of classifying them as policy violations.

Since GPT-5.6 Sol works correctly with the same account, Codex runtime, machine, and prompt, GPT-6 Astra should behave similarly unless the prompt actually violates policy.

The account should also behave consistently across devices instead of receiving `invalid_prompt` for every GPT-6 Astra request.

### Additional information

The problem follows the OpenAI account across different computers.

This makes a machine-specific installation issue unlikely. It may be related to GPT-6 Astra account routing, rollout/entitlement state, or Astra-specific safety classification.

Start by reproducing the issue with the documented codex exec commands using gpt-6-astra and the working gpt-5.6-sol control. Compare behavior across reasoning efforts and account or device conditions; done means harmless prompts are accepted by Astra without the invalid_prompt policy error.